Compact forced warm air furnace

ABSTRACT

A furnace for a forced warm air heating system capable of multipoise installation, including an outer jacket, an inner jacket, a heat exchanger within the inner jacket enclosing a combustion zone, and a burner assembly producing combustion within the heat exchanger. A supply air blower is arranged within the outer jacket to propel return air along a return path beside the inner jacket through the space between the inner and outer jackets and circulate the air within the inner jacket along a supply path in counterflow relation to the return air path. A combustion air blower may be driven from the same shaft as the supply air blower to provide air for the burner assembly.

United States Patent Solka et a1. [45] May 16, 1972 [54] COMPACT FORCEDWARM AIR 3,481,321 12/1969 Reichelderfer ..126/116 x FURNACE [72]Inventors James L Solka Bridgewater Charles A FOREIGN PATENTS ORAPPLICATIONS Reiche'derter, Harrisonburg; John J. 1,196,671 5/1959France 126 I0 AA Dieckmann, l-larrisonburg; Anthony M. c n Harrisonburg,a of Primary Examiner-Charles J. Myhre Attorney--Mason, Fenwick &Lawrence [73] Ass1gnee: Dunham-Bush, lnc., Harrisonburg, Va.

22 Filed: June 25, 1970 [571 ABSTRACT 21 APPL 49 732 A furnace for aforced warm air heating system capable of multipoise installation,including an outer jacket, an inner jacket, a heat exchanger within theinner jacket enclosing a [52] US. Cl ..126/1l0 R comb'ustion zone and aburner assembly producing [51] Int. Cl ..F24h 3/02 bustion within theheat exchanger A Supp, air blower i an [58] Field 0 Search 10, B, 116,ranged within the Outer j k to p p l return i along a 126/ l 16 A returnpath beside the inner jacket through the space between [56] ReferencesCited the inner and outer jackets and circulate the air within the innerjacket along a supply path in counterflow relation to the UNITED STATESPATENTS return air path. A combustion air blower may be driven from thesame shaft as the supply air blower to provide air forth 2,658,503 111953 Sch'eurer..... ..126/110 bumerassembly 2,089,407 8/1937 Norris..l26/l10 2,263,098 11/1941 Mueller ..126/110 6 Claims, 4 DrawingFigures PATENTEBMY 16 I972 3.662. 738

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SHEET 2 OF 3 INVENTORS JAMES L.SOL.KA, CHARLES A-EEKZHELSERFEQ, JoanJ-DECKMANN vii/ANTHONY M-CAs-rE LLO Was fw i'wdxQJ Wee ATTORNEYSPATENTEDMAHSIQn SHEET 3 [1F 3 S s R Y m R m m E m V F m a 0 M AE L A K0L LLNE omuwem QWKAMHALKS aEcM. m M DY a?" m 0 v QNH J AH YM Ho CIA W Thepresent invention relates in general to forced warm air furnace systems,and more particularly to a compact high velocity forced warm air furnacehaving relatively restricted combustion space, especially designed foruse with a high velocity system including a larger diameter plenum pipeand relatively small diameter flexible air ducts with an unencumberedoutlet and close coupled attenuator such as disclosed in co-pendingapplication Ser. No. 866,052, now U.S. Pat. No. 3,575,234 filed Aug. 22,l969'by John J. Dieckmann, one of the joint inventors named in thepresent application.

Design of compact furnaces which will provide efficient heating,particularly for combustion of natural gas, wherein the furnace is oflow cost construction, compact configuration,-and is simple and easy toinstall, making it especially suitable for use in modular homes orfactory built home construction, has been recognized as a desirable andneeded objective. However, furnace construction heretofore has beenrelatively larger in size or overall dimension and oftentimes complexand not particularly suitable for such installations or adaptable to theeasily installed high velocity small duct system and require differentmodels for different positions.

An object of the present invention is the provision of a novel forcedwarm air furnace construction, particularly for use in high velocity airconditioning systems, which will be compact and of low cost andrelatively simple construction, and wherein the design of the furnaceand all controls are such that the same unit, without modificationondesign changes, can be used inmultipoise configurationsmhat is thefurnace can be installed as an upflow, a counterflow, or a horizontalunit.

Another object of the present invention is the provision of a compactforced warm air furnace which includes an integral compartment providingthe necessary cavity for optionally sliding in a cooling coil assemblywhen desired to provide both a heating and cooling system.

Another object of the-present invention is the provision of a compactforced Warm air furnace, particularly for use in high velocity heatingsystems, wherein the furnace provides an integral return air duct ordrop by bringing return air over the outside of an enclosed heatexchanger compartment, the return to the furnacebeing-on top of the unitadjacent to the discharge or supply connection.

Another object of the present invention is theprovision of novel compactforced warm air furnace 'wherein the burner is readily adaptable forproviding sealed combustion, wherein the combustion air for the burnermay be brought in through a separate blower which provides forconnecting to a completely ducted system from the outside of the room inwhich the furnace is installed, commonly outside air.

Another object of the present invention is the provision of a novelcompact forced warm air furnace wherein the burner and blower componentsare designed to be usedwith a compact heat exchanger such as the typedisclosed in U.S. Pat. No. 3,481,321 granted to Charles A.Reichelderfer, one of the joint inventors of the present application,providing a furnace characterized by extreme compactness and highlyefficient combustion characteristics.

Another object of the present invention is the provision of a compactformed warm air furnace wherein, by nature of the return air systemprovided, the furnace has a .built in filter system so that no externalfilter rack or filter grille isrequired.

Other objects, advantages and capabilities of the present invention willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings illustrating a preferredembodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a fragmentary perspectiveview, illustrating a furnace constructed in accordance with the presentinvention and fragmentary portions of the return air drop and the supplyduct components to be assembled therewith;

FIG. 2 is a perspective view of the furnace, with portions of the sidewalls broken away, illustrating the internal components thereof and thecirculation of air through the interior of the furnace housing;

FIG. 3 is a fragmentary perspective view, to enlarged scale, withportions broken away, illustrating the supply air blower, thecombustionair blower, the burner assembly and the heat exchanger, witharrows indicating combustion air circulation and supply air circulationtherethrough; and

FIG. 4 is a vertical section view through the blowers and the motortherefor, taken along the line 4-v-4 of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT While the forcedwarm airfurnace of the presentinvention is suitable for operation in anydirection of air flow, upward, downward-or horizontal, forpurposes ofconvenience of illustration and to describe its operation in the mostsimple manner, the following description is directed to an embodimentwherein the air flow is vertically upward.

Referring to the drawings, wherein like reference characters designatecorresponding parts throughout'the several figures, the furnace,generally indicated by the reference character 10, forms a hot airgenerator and employs an essentially airtight outer jacket or wrapper ll enclosing three sides of the generator 10, having side panels 12 and13, rear panel 14, top panel 15 and bottom panel 16. The front or fourthside of the enclosure isprovided with upper and lower front panelsections 17Aand 17B, and a readily dismountable, louvered access panel17C in the vertical midregion thereof. Within the outer jacket 11, ahorizontal partition 18 extends from approximately the lower edge of theremovable access panels 17C to.the midregion of the jacket, to underlapthe horizontal surface portion of the corner recess or rabbit 19 of aninner jacket or enclosure casing 20 which forms an enclosure for a heatexchanger unit 21. The enclosure defined by the casing 20 is of invertedL-shaped configuration, providing an upper lateral extension 20Aprojecting forwardly to the front panel 17A of the jacket. The innercasing 20 additionally includes a lower front wall section"20B, whichmay be spaced rearwardly slightly from a vertical mounting plate 22 on,which the burner assembly 23, to be later described, is supported,.andincludes a rear wall 20C spaced inwardly from the rear panel '14 oftheouter jacket, and side walls 20D and 20Erespectively spaced inwardlyfrom the side panels 12 and 13 of the jacket 11. The bottom of thedepending leg portion of the intermediate casing 20 defined by the walls20D through 20E is also closed by delivered to the jacket 11 through areturn air duct or drop 25,

shown here of rectangular cross-section near the furnace,

. which is sealed to a rectangular return air. opening 26 inthe toppanel15 so that the return air is delivered downwardly through the outerjacket or wrapper 11 to the lower region thereof by being returned overthe outside of theinner jacket or enclosure casing20 enclosing the heatexchanger compartment. The heat exchanger 21 is preferably of theconstruction disclosed in said earlier U.S. Pat. No. 3,481,321 grantedDec.

passagesZlA extending vertically therethrough open at the bottom and thetop and bounded'by corrugated walls as disclosed in said earlier patent.The air passages 21A are located in one of the leg portions of thegenerally U-shaped configuration defined by the middle air passage 21A(the one to the left of the passage 21A. as viewed in FIG. 2) while theother leg to the near or right hand side of the passage 21A as viewed inFIG. 2 communicates with the burner assembly 23.

As the inner jacket 20 forming the enclosure for the heat exchangercompartment is spaced inwardly from the walls of the outer jacket orwrapper 11, the return air descending through the return air duct 25 andopening 26 is conveyed downwardly through the outer return compartmentdefined in the space between the jackets 1 l and 20 to the lower chamber27 of the furnace below the partition 18 and the bottom 20F of the innerjacket 20. This serves the dual purpose of providing a film of air nearroom temperature adjacent to the walls of the outer jacket 11, making itpossible to design for zero clearances without the need for insulationat additional cost, and also gives good acoustical attenuation tominimize the transmission of noise and thus enhance the acousticalcharacteristics of the unit without significantly increasing the size ofthe unit.

Mounted on the underside of the horizontal partition 18 and within thelower chamber 27 is a supply air blower 28, comprising a conventionalblower scroll 29 having its discharge outlet portion 29A communicatingwith an opening 29B in the wall of the comer recess or rabbit 19 of theinner jacket 20 for passage of the supply air streams generated by therotary impeller 30 of the blower 28 to the space within the inner jacket20 below the heat exchanger 21 for passage of the supply air upwardlyabout the outer walls of the heat exchanger 21 and also through the airpassages 21A and 21A thereof. The blower scroll 29 is provided with theusual circular air inlet 29C concentric with the axis of the impeller todraw the return air from the lower chamber 27 into the center region ofthe blower scroll and discharge the same as supply air through thedischarge outlet portion 29A and opening 298 into the inner jacket 20.The impeller 30 is supported on a vertical shaft 31, which is driven byan electric motor 32 supported in depending relation below the scroll29, as by supporting bracket members or straps 33.

A combustion air blower 34 is mounted on the upper surface of thehorizontal partition 18, and is also driven by the same motor 32 toreduce the number of operating units in the system, improve servicereliability, and help give a more compact unit. To this end, theimpeller 35 of the blower 34 is mounted on an upper portion or extension31A of the shaft 31 which rises through an opening in the horizontalpartition 18, and is located within a blower scroll 36 mounted on thehorizontal partition 18, having a circular air inlet 36A in the upperwall portion thereof concentric with the projected axis of the shaft 31and having an air discharge outlet 36B connected to an air tube orconduit 37 which supplies the pressurized combustion air stream to theburner assembly 23.

The burner 23 may be of conventional construction having an air inletplenum 23A communicating with the air tube 37 for supplying thecombustion air to the burner which receives fuel through a fuel supplyconduit 233. The upper burner portion may, for example, be ofcylindrical configuration of the construction illustrated in theco-pending patent application Ser. No. 738,920 filed June 21, 1968 byCharles A. Reichelderfer and Frederick L. Runninger.

By virtue of the compact heat exchanger 21 and the power burner 23supplied with combustion air under pressure, the furnace can utilize avery small diameter venting system, for example a two inch flue exhaust,as indicated at reference character 38, extending from the front wallportion of the heat exchanger to the left of the medial axis or airpassage 21A thereof, as viewed in FIG. 2, through the vertical mountingplate 22 and outwardly through one of the walls of the outer jacket 11,for example the side wall 13. The small diameter vent 38 gives reducedstack losses as compared to the usual four or inch vent which would beemployed for the same size conventional furnace, and also providessignificant cost savings to the installer.

Reviewing the overall air flow patterns through the furnace, the returnair descending through the return air duct 25 enters the opening 26 andis diverted laterally and rearwardly as indicated by the arrows 39 tothe sides and rear of the inner jacket 20 forming the enclosure for theheat exchanger compartment, providing a film of return air near roomtemperature inwardly along the side and rear walls of the outer jacket11. The outer return compartment defined between the walls of the outerjacket 11 and the inner jacket 20 also minimizes direct radiation ortransmission of noise from the furnace itself and gives good acousticalattenuation. Further improvement in the acoustical characteristics canbe obtained, if desired, by coating the insides of the walls of thejacket 11 with sound deadening material. Also, the disposition of theblowers 28 and 34 deep inside the unit with no direct communication tooutside openings eliminates direct noise transmission.

The return air descending below the bottom of the inner jacket 20 intothe lower chamber 27, as indicated by arrows 40, is drawn upwardlythrough the air inlet 29C of the supply air blower scroll 29 andimpelled by the impeller 30 as a supply air stream, indicated by arrows41, through the discharge outlet portion 29A and opening 298 into theinterior of the inner casing 20 to rise about the outer walls of theheat exchanger 21 and through the air passages 21A, 21A to be heated bythermal exchange with the heat dispensing gas stream within the heatexchanger. The thus heated supply air, indicated by the arrows 42 passthrough the upper compartment or cavity within the inner jacket 20 andabove the heat exchanger 21 into the supply air duct 24, which may forexample be a 7 inch diameter supply duct, which delivers the heated airto a distribution system, such for example as a plenum distribution box43 and branch air conveying ducts 44 delivering the high velocityconditioned air to terminator devices in the rooms or spaces to beconditioned. The total configuration of the power burner with smalldiameter vent, compact heat exchanger, low stand by losses, and lowcasing losses due to return air coming over the outside of the heatexchanger enclosure gives a significantly higher overall efiiciencycompared to conventional systems. A heat transfer combustion efficiencyof about percent in actual operation is obtainable, compared to about 75percent for conventional gas fired heating systems. With such a design,the compact heat exchanger and burner assembly can be made out ofstainless steel, which is prohibitively costly in the larger lesscompact conventional designs. It will be appreciated by those skilled inthe art that the use of stainless steel for these components would givelonger life and eliminate corrosion problems and future fieldreplacement.

The design provides a compartment or cavity above the heat exchanger andwithin the enclosure defined by the inner jacket 20, which mayoptionally accomodate a cooling coil assembly when it is desired toprovide both a heating and cooling system served by the conditioned airgenerator 10.

The combustion air supply for the burner assembly 23 may be either drawnfrom the environment in which the furnace is installed by drawing airthrough the louvered access panel 17C and the inlet 36A of thecombustion air blower scroll 36, or the inlet of the blower scroll 36can be connected through an optional separate air duct to airoriginating outside of the room in which the furnace is installed,commonly outside air, for providing sealed combustion. For example,combustion air for the burner may be brought in through a completelyducted system from outside of the furnace room, for example a ductedsystem which receives outside air and delivers it to the inlet of thecombustion air blower 34. There are advantages for such sealedcombustion in the modular home and the mobile home industries, and wherelocal codes dictate that combustion air should not be brought from theenvironment in which the furnace is installed.

The design of the present furnace also reduces to a minimum the timerequired to install the furnace, because of the simple supply and returnconnections, which are made at the top of the unit in the upflowposition. Conventional upflow furnace configurations typically have along return air drop to the bottom of the unit that must be providedadjacent to the furnace, whereas the length of the air drop is greatlyreduced by the present furnace design.

The present furnace is characterized by a very low amount of floor spaceto be consumed for installation, which makes it particularly suitablefor modular and mobile home construction where space saving isespecially important. Typically, a 60,000 Btu per hour input unit wouldhave about 2% square feet of floor area, while 80 and 100,000 Btu perhour input units would consume about 2.8 square feet of floor space. Thedepth of the unit is minimized to about 23 inches, and as such it can beput into closets and vestibules that are common to the mobile homeindustry.

It will be apparent that while the foregoing description has beendirected to a gas fired unit, the basic design can be employed for oilfired or electrical power heating systems, and the furnaces with thisbasicdesign may be employed in low velocity more conventional types ofheating systems as well as to high velocity air heating systems.

What is claimed is:

l. A furnace for a forced warm air heating system comprising an outercasing having first and second ends perpendicular to an axis and sidesparalleling said axis defining a first enclosure, said first end havingan air return opening therein, an inner jacket defining a secondenclosure having end and side panels spaced inwardly from said ends andsides providing a return air inlet chamber and a second chamber adjacentsaid first and second ends, respectively, and side enveloping passagestherebetween for conveying return air along first flow paths parallelingsaid axis from said inlet chamber to said second chamber, a heatexchanger located within said jacket having heat exchange walls formingan enclosure about a combustion zone, a burner assembly for producingcombustion of fuel and air mixture in the combustion zone, a supply airduct communicating through said first end with the adjacent end panel ofsaid inner jacket for conveying heated air from the inner jacket torooms to be heated, a motor driven supply air blower having an inletcommunicating with said second air chamber and an outlet communicatingwith the interior of the inner jacket for impelling return air alongsaid first flow paths to said second chamber and circulating the samewithin said inner jacket along counterflow paths relative to said firstflow paths adjacent said heat exchange walls to heat the air anddischarge the heated air through said supply air duct, a combustion airblower having a rotary impeller communicating with air externally ofsaid second chamber and with said burner assembly for supplyingcombustion air under pressure to the burner assembly, said supply airblower including a rotary impeller in said second chamber supported on acommon axis of rotation with the impeller of the combustion air blower,and a single motor connected to both of said impellers for concurrentlyrotating the latter. I V

2. A furnace as defined in claim 1, wherein said heat exchanger is ofgenerally box-like cubic configuration having outer side walls spacedinwardly from the side panels of said inner jacket for flow of blowerdischarge air therebetween and having intermediate flue channelstherethrough for passage of the blower discharge air through the fluechannels in intimate thermal exchange relation with flue-bounding wallsgenerally paralleling said outer side walls.

3. A furnace for a forced warm air heating system comprising an outercasing having a top wall, a bottom and vertical side walls defining afirst enclosure, said top wall having an air return opening thereinconnected to a return duct and having a supply duct extendingtherethrough, an inner jacket defining a second enclosure having top,bottom and side panels spaced inwardly from the top, bottom and sides ofthe outer casing and defining a blower chamber below the jacket, theside walls and side panels defining uninterrupted air channelstherebetween substantially coextensive with said side panels fordownward flow of return air to the blower chamber from said return ductalong downward flow paths enveloping three sides of the jacket as a filmof return air, a heat exchanger located within said jacket having heatexchange walls forming an enclosure about a combustion zone, a burnerassembly for producing combustion of fuel and air mixture in thecombustion zone, said supply duct communicating with the top panel ofsaid inner jacket for conveying heated air from the inner jacket torooms to be heated, a motor driven supply air blower having an inletopening into said blower chamber to receive air therefrom and a scrolldischarge outlet communicating with the interior of the inner jacket forcirculating return air along said return flow paths to said blowerchamber and propelling the air in upward counterflow paths within thejacket relative to said downward flow paths for passage into thermalexchange relation with said heat exchanger and discharge through saidsupply duct, a combustion air blower having a rotary impellercommunicating with air externally of said blower chamber and with saidburner assembly for supplying combustion air under pressure to theburner assembly, said supply air blower including a rotary impeller insaid blower chamber supported on a common axis of rotation with theimpeller of the combustion air blower, and a single motor connected toboth of said impellers for concurrently rotating the latter.

4. A furnace as defined in claim 3 wherein said heat exchanger is ofgenerally box-like cubic configuration having outer side walls spacedinwardly from the side panels of said inner jacket for flow of blowerdischarge air therebetween and having intermediate flue channelstherethrough for passage of the blower discharge air through the fluechannels in intimate thermal exchange relation with flue-bounding wallsgenerally paralleling said outer side walls.

5. A furnace for a forced warm air heating system comprising an outercasing having a top wall, a bottom and vertical side walls defining afirst enclosure, said top wall having an air return opening thereinconnected to a return duct and having a supply duct extendingtherethrough, an inner jacket defining a'second enclosure having top,bottom and side panels spaced inwardly from the top, bottom and sides ofthe outer casing and defining a blower chamber below the jacket, theside walls and side panels defining uninterrupted air channelstherebetween substantially coextensive with said side panels fordownward flow of return air to the blower chamber from said return ductalong downward flow paths enveloping three sides of the jacket as a filmof return air, a heat exchanger located within said jacket having heatexchange walls forming an enclosure about a combustion zone, a burnerassembly for producing combustion of fuel and air mixture in thecombustion zone, said supply duct communicating with the top panel ofsaid inner jacket for conveying heated air from the inner jacket torooms to be heated, a motor driven supply air blower having an inletopening into said blower chamber to receive air therefrom and a scrolldischarge outlet communicating with the interior of the inner jacket forcirculating return air along said return flow paths to said blowerchamber and propelling the air in upward counterflow paths within thejacket relative to said downward flow paths for passage into thermalexchange relation with said heat exchanger and discharge through saidsupply duct, wherein said inner jacket is of inverted, substantiallyL-shaped configuration in side elevation having an upper horizontal legportion substantially coextensive in length to the fore-and-aft depth ofsaid outer casing and a depending vertical leg portion extendingtherebelow of a considerably shallower for-and-aft depth disposing therearmost vertical surfaces thereof in vertical alignment and defining aburner chamber between front wall portions of said vertical leg andouter casing, said heat exchanger being located wholly in said dependingvertical leg portion, and said horizontal leg portion providing a cavityfor reception of a cooling coil assembly in said upward counterflowpaths of air propelled by said blower.

6. A furnace as defined in claim 13, wherein said heat exchanger is ofgenerally box-like cubic configuration having outer side walls spacedinwardly from the side panels of said inner jacket for flow of blowerdischarge air therebetween and having intermediate flue channelstherethrough for passage of the blower discharge air through the fluechannels in intimate thermal exchange relation with flue-bounding wallsgenerally paralleling said outer side walls.

1. A furnace for a forced warm air heating system comprising an outercasing having first and second ends perpendicular to an axis and sidesparalleling said axis defining a first enclosure, said first end havingan air return opening therein, an inner jacket defining a secondenclosure having end and side panels spaced inwardly from said ends andsides providing a return air inlet chamber and a second chamber adjacentsaid first and second ends, respectively, and side enveloping passagestherebEtween for conveying return air along first flow paths parallelingsaid axis from said inlet chamber to said second chamber, a heatexchanger located within said jacket having heat exchange walls formingan enclosure about a combustion zone, a burner assembly for producingcombustion of fuel and air mixture in the combustion zone, a supply airduct communicating through said first end with the adjacent end panel ofsaid inner jacket for conveying heated air from the inner jacket torooms to be heated, a motor driven supply air blower having an inletcommunicating with said second air chamber and an outlet communicatingwith the interior of the inner jacket for impelling return air alongsaid first flow paths to said second chamber and circulating the samewithin said inner jacket along counterflow paths relative to said firstflow paths adjacent said heat exchange walls to heat the air anddischarge the heated air through said supply air duct, a combustion airblower having a rotary impeller communicating with air externally ofsaid second chamber and with said burner assembly for supplyingcombustion air under pressure to the burner assembly, said supply airblower including a rotary impeller in said second chamber supported on acommon axis of rotation with the impeller of the combustion air blower,and a single motor connected to both of said impellers for concurrentlyrotating the latter.
 2. A furnace as defined in claim 1, wherein saidheat exchanger is of generally box-like cubic configuration having outerside walls spaced inwardly from the side panels of said inner jacket forflow of blower discharge air therebetween and having intermediate fluechannels therethrough for passage of the blower discharge air throughthe flue channels in intimate thermal exchange relation withflue-bounding walls generally paralleling said outer side walls.
 3. Afurnace for a forced warm air heating system comprising an outer casinghaving a top wall, a bottom and vertical side walls defining a firstenclosure, said top wall having an air return opening therein connectedto a return duct and having a supply duct extending therethrough, aninner jacket defining a second enclosure having top, bottom and sidepanels spaced inwardly from the top, bottom and sides of the outercasing and defining a blower chamber below the jacket, the side wallsand side panels defining uninterrupted air channels therebetweensubstantially coextensive with said side panels for downward flow ofreturn air to the blower chamber from said return duct along downwardflow paths enveloping three sides of the jacket as a film of return air,a heat exchanger located within said jacket having heat exchange wallsforming an enclosure about a combustion zone, a burner assembly forproducing combustion of fuel and air mixture in the combustion zone,said supply duct communicating with the top panel of said inner jacketfor conveying heated air from the inner jacket to rooms to be heated, amotor driven supply air blower having an inlet opening into said blowerchamber to receive air therefrom and a scroll discharge outletcommunicating with the interior of the inner jacket for circulatingreturn air along said return flow paths to said blower chamber andpropelling the air in upward counterflow paths within the jacketrelative to said downward flow paths for passage into thermal exchangerelation with said heat exchanger and discharge through said supplyduct, a combustion air blower having a rotary impeller communicatingwith air externally of said blower chamber and with said burner assemblyfor supplying combustion air under pressure to the burner assembly, saidsupply air blower including a rotary impeller in said blower chambersupported on a common axis of rotation with the impeller of thecombustion air blower, and a single motor connected to both of saidimpellers for concurrently rotating the latter.
 4. A furnace as definedin claim 3 wherein said heat exchanger is of generally box-like cubicconfiguraTion having outer side walls spaced inwardly from the sidepanels of said inner jacket for flow of blower discharge airtherebetween and having intermediate flue channels therethrough forpassage of the blower discharge air through the flue channels inintimate thermal exchange relation with flue-bounding walls generallyparalleling said outer side walls.
 5. A furnace for a forced warm airheating system comprising an outer casing having a top wall, a bottomand vertical side walls defining a first enclosure, said top wall havingan air return opening therein connected to a return duct and having asupply duct extending therethrough, an inner jacket defining a secondenclosure having top, bottom and side panels spaced inwardly from thetop, bottom and sides of the outer casing and defining a blower chamberbelow the jacket, the side walls and side panels defining uninterruptedair channels therebetween substantially coextensive with said sidepanels for downward flow of return air to the blower chamber from saidreturn duct along downward flow paths enveloping three sides of thejacket as a film of return air, a heat exchanger located within saidjacket having heat exchange walls forming an enclosure about acombustion zone, a burner assembly for producing combustion of fuel andair mixture in the combustion zone, said supply duct communicating withthe top panel of said inner jacket for conveying heated air from theinner jacket to rooms to be heated, a motor driven supply air blowerhaving an inlet opening into said blower chamber to receive airtherefrom and a scroll discharge outlet communicating with the interiorof the inner jacket for circulating return air along said return flowpaths to said blower chamber and propelling the air in upwardcounterflow paths within the jacket relative to said downward flow pathsfor passage into thermal exchange relation with said heat exchanger anddischarge through said supply duct, wherein said inner jacket is ofinverted, substantially L-shaped configuration in side elevation havingan upper horizontal leg portion substantially coextensive in length tothe fore-and-aft depth of said outer casing and a depending vertical legportion extending therebelow of a considerably shallower for-and-aftdepth disposing the rearmost vertical surfaces thereof in verticalalignment and defining a burner chamber between front wall portions ofsaid vertical leg and outer casing, said heat exchanger being locatedwholly in said depending vertical leg portion, and said horizontal legportion providing a cavity for reception of a cooling coil assembly insaid upward counterflow paths of air propelled by said blower.
 6. Afurnace as defined in claim 13, wherein said heat exchanger is ofgenerally box-like cubic configuration having outer side walls spacedinwardly from the side panels of said inner jacket for flow of blowerdischarge air therebetween and having intermediate flue channelstherethrough for passage of the blower discharge air through the fluechannels in intimate thermal exchange relation with flue-bounding wallsgenerally paralleling said outer side walls.